Signal transduction of the protective effect of insulin like growth factor-1 on adriamycin-induced apoptosis in cardiac muscle cells

Cardiomyocyte Atrophy, an Underestimated Contributor in Doxorubicin-Induced Cardiotoxicity

Left ventricular (LV) mass loss is prevalent in doxorubicin (DOX)-induced cardiotoxicity and is responsible for the progressive decline of cardiac function. Comparing with the well-studied role of cell death, the part of cardiomyocyte atrophy (CMA) playing in the LV mass loss is underestimated and the knowledge of the underlying mechanism is still limited. In this review, we summarized the recent advances in the DOX-induced CMA. We found that the CMA caused by DOX is associated with the upregulation of FOXOs and “atrogenes,” the activation of transient receptor potential canonical 3-NADPH oxidase 2 (TRPC3-Nox2) axis, and the suppression of IGF-1-PI3K signaling pathway. The imbalance of anabolic and catabolic process may be the common final pathway of these mechanisms. At last, we provided some strategies that have been demonstrated to alleviate the DOX-induced CMA in animal models.

The Akt1 isoform is an essential mediator of ischaemic preconditioning

Phosphatidyl-inositol-3-kinase (PI3K)-Akt pathway is essential for conferring cardioprotection in response to ischaemic preconditioning (IPC) stimulus. However, the role of the individual Akt isoforms expressed in the heart in mediating the protective response to IPC is unknown. In this study, we investigated the specific contribution of Akt1 and Akt2 in cardioprotection against ischaemia-reperfusion (I-R) injury. Mice deficient in Akt1 or Akt2 were subjected to in vivo regional myocardial ischaemia for 30 min. followed by reperfusion for 2 hrs with or without a prior IPC stimulus. Our results show that mice deficient in Akt1 were resistant to protection with either one or three cycles of IPC stimulus (42.7 ± 6.5% control versus 38.5 ± 1.9% 1 χ IPC, N = 6, NS; 41.4 ± 6.3% control versus 32.4 ± 3.2% 3 χ IPC, N = 10, NS). Western blot analysis, performed on heart samples taken from Akt1^−/− mice subjected to IPC, revealed an impaired phosphorylation of GSK-3β, a downstream effector of Akt, as well as Erk1/2, the parallel component of the reperfusion injury salvage kinase pathway. Akt2^−/− mice, which exhibit a diabetic phenotype, however, were amenable to protection with three but not one cycle of IPC (46.4 ± 5.6% control versus 35.9 ± 5.0% in 1 χ IPC, N = 6, NS; 47.0 ± 6.0% control versus 30.8 ± 3.3% in 3 χ IPC, N = 6; *P = 0.039). Akt1 but not Akt2 is essential for mediating a protective response to an IPC stimulus. Impaired activation of GSK-3β and Erk1/2 might be responsible for the lack of protective response to IPC in Akt1^−/− mice. The rise in threshold for protection in Akt2^−/− mice might be due to their diabetic phenotype.

Saeng-Ji-Hwang has a protective effect on adriamycin-induced cytotoxicity in cardiac muscle cells

This study examined the effect of Saeng-Ji-Hwang (SJH: Radix Rehmanniae) on cardiac muscle cells. Adriamycin-exposed H9C2 cardiac muscle cells were treated with a water extract of SJH. The adriamycin induced cell death and caspase-3 activation were significantly inhibited by SJH (2 mg/ml), which can be explained by the increase in Bcl-2 expression and the inhibition of Bax expression. Adriamycin reduced the Mn-SOD protein expression level in H9C2 cardiac muscle cells but a SJH treatment partially but significantly reversed this effect. Manganese (Mn)-TBAP or Mn-TMyM--mitochondria-specific SOD mimetic agent--reduced the adriamycin-induced cytotoxicity. It was also shown that SJH inhibits the release of H2O2 and prevents lipid peroxidation in the presence of adriamycin. This study examined the intracellular GSH level, which showed that adriamycin significantly decreased the intracellular GSH level but SJH increased it. BSO, a selective inhibitor of glutamyl cysteinyl ligase, which is a rate-limiting enzyme in GSH synthesis, did not affect the viability of the cardiac muscle cells. However, a combination of BSO with SJH in the presence of adriamycin reversed the SJH-induced protection. Overall, the results suggest that SJH-associated Mn-SOD and GSH are important factors in the mechanism of the SJH-induced protective mechanism in H9C2 cardiac muscle cells.